So it looks like I think I may have temporarily found the issue. It seems to be an issue with iOS 15, just my theory.
If the admins want to merge this post with another post I made , I think they relate now. I did a comparison of videos between iPhone and Mac, since the difference was small in number 472 vs 449. In turns out that on my iPhone, these were all videos that were shared with me that the Apple/Messages/iOS 15 was able to pick up. For whatever the reason, it shows up on my iPhone with 472 videos, once I started saving them, the numbers on my mac increased. Eventually, once all the videos had been saved through Photos, the Mac and iPhone both matched up.
Then I went to the iPad, to see the issue there, it turns out there were some videos that had that message bubble on the iPad, once I started saving those, then the numbers on my iPhone because to line up.
I am not sure what Apple was thinking, because something helpful that would have been nice, if there was a way to just filter those videos and do a bulk ‘save’. But that’s not an option, maybe there is some shortcut that can be created or that exists.
Anyhow, these are my findings so far for those who are interested.